SRAM 2-speed auto shift gear/hub motor

[Kudoscycles]

I first saw this combined motor with a 2 speed internal auto shifting gear at the SRAM stand at Eurobike 2012. It seemed an interesting idea except that the salesman advised that the motor,to avoid sudden torque input,would not power up until the road speed exceeded 4mph.
I notice there is a new company named Momentum e-bikes,exhibiting at the London Excel Cycle show,who appear to be combining this motor hub with a torque pedal sensor.
I just cannot understand how hill climbing would be possible with this combination. Hill starts would require some effort to get to that 4mph,especially using a torque sensor, and with only 2 gears the step split into top gear would be massive.
Has anyone any experience of this e-bike because I just cannot understand how it can work?
Please understand not being negative to a another manufacturers product,especially one with innovative ideas but I genuinely cannot understand the practicality of the technology?
Happy new year everyone,I feel good about 2013-so much interesting ventures already planned.
Dave
Kudoscycles

 

[muckymits]

you will be joining wurly

 

[funkylyn]

I first saw this combined motor with a 2 speed internal auto shifting gear at the SRAM stand at Eurobike 2012. It seemed an interesting idea except that the salesman advised that the motor,to avoid sudden torque input,would not power up until the road speed exceeded 4mph.
I notice there is a new company named Momentum e-bikes,exhibiting at the London Excel Cycle show,who appear to be combining this motor hub with a torque pedal sensor.
I just cannot understand how hill climbing would be possible with this combination. Hill starts would require some effort to get to that 4mph,especially using a torque sensor, and with only 2 gears the step split into top gear would be massive.
Has anyone any experience of this e-bike because I just cannot understand how it can work?
Please understand not being negative to a another manufacturers product,especially one with innovative ideas but I genuinely cannot understand the practicality of the technology?
Happy new year everyone,I feel good about 2013-so much interesting ventures already planned.
Dave
Kudoscycles

Would you like to post some technical pictures too so that we get the full story in its full technical glory Dave ?

Happy new year !

Lynda

 

[muckymits]

Stirrer

 

[funkylyn]

Stirrer

ME ??
Watch it you wannabe Geordie......

Very sorry Dave for hijacking your post......its ok, Im going to bed now

Lynda

 

[Kudoscycles]

Would you like to post some technical pictures too so that we get the full story in its full technical glory Dave ?

Happy new year !

Lynda

Lynda,sorry can't supply-Momentum's website has little technical info. I have got some info from SRAM website, there is a bike named Townie in the states which appears to have a few reviews-but all reviews are really only a repeat of Sram's publicity info,no riding experience. I understand the switch point from low to high gear is set at 10mph and is automatic.
The torque sensor appears to be built into the hub.
I am trying to visualise a typical riding pattern-hill start straining up to 4 mph,power comes in,ride up to 10mph,bike changes into high gear,rider straining speed drops off,bike changes into lower gear,ride becomes easier exceeds 10mph,rider straining speed drops off.....and so on.
I can see on the flat the simplicity of the system would work and maybe I haven't fully understood the system but I cannot understand it coping with our variable terrain.
Trans-X of Taiwan exhibited a 7 speed fully auto bike transmission at Eurobike 2011 but I didn't see it at the 2012 event.
Dave
Kudoscycles

 

[mike killay]

Years ago I had a Mobylette moped that had this 4mph business. At first you had to pedal to 4mph to turn the engine over to get it firing. That was hard enough.
Then, even with the engine running, the automatic clutch would not engage until you got it up to 4mph.
Frankly, it was a ridiculous idea. I live in a hilly town and the thing was useless if you had to stop for traffic lights etc on a hill.

 

[jerrysimon]

Well getting technical.... I was looking at their web site

http://www.momentumelectric.com/shop/upstart/

Looks like the tensioner on the chain measures the torque. Seems a little over complicated to me.

The SRAM A2 is a new re modeling (they were popular in the 60/70s) and is basically a self contained hub with no cables that simply changes up and down two gears when it goes above or below a set speed. I have been using one on my daily commute for over a year. I retro fitted it to my Brompton and took it apart so it changes up gear at 10mph. Obviously the change speed it set by the wheel size so needs to be adjusted for smaller wheels.

I basically just start off using a little throttle if required and when I hit 10mph it changes up to the higher gear. Obviously when you stop/drop down to below 10mph it then goes down to the lower gear automatically. It works perfectly with my Tongxin fitted, throttle controlled Brompton

Regards

Jerry

 

[funkylyn]

Thanks for that very clear technical explanation jerry.......I actually understood every word you said........I think......but how is it on HILLS ?

Lynda

 

[jerrysimon]

Lynda and that was a very observant and good question.

The simple answer is what hills ? I live in Cambridge

I think on steep hills (without assistance) it could be a challenge, though as long as you keep pressure on the pedals it remains in the lower gear even if you exceed 10mph when you are going up a hill.

Regards

Jerry

 

[Electrifying Cycles]

Hi

I am aware A to B gave them a very favourable review. Could be worth checking out.

DW

 

[Kudoscycles]

I found a video that the marketing guy responsible for Electra Townie e-bike in the states,it uses that Sram hub on a 'flat foot' bike. Despite him describing himself as an e-bike engineer of years standing I am afraid he lost credibility when the interviewer asked him the voltage of the e-bike and he didn't know it!
The concept of 'flat foot' riding with a patented crank moved forwards is so American marketing hype-I thought that the most efficient riding position was the centre of effort over the centreline of the pedals on the downstroke-just cannot imagine riding a bicycle 'Harley' position.
The whole concept seems to be leaning towards short distance cycling on the flat, riding your armchair-surely that is the exact opposite of what most of us buy an e-bike for. I notice the interviewer never questioned about hills!
Will try to get that video loaded.
Dave

 

[flecc]

You ask why only two gears Dave?

As you know, the optimum climb speed on existing hub motors is at approximately half full speed, so on legal e-bikes at around 8 mph. Since there's a minimum practical cycling speed, it's only necessary for the motor to have a second gear shifting that optimum climb speed to about 5 mph to have the ability to climb most hills.

The current practice on crank drives of the motor using all the bike's gears is a far from ideal compromise. The rider needs lots of gears to have comfortable cycling rhythm in all circumstances, the electric motor doesn't.

 

[Old_Dave]

The rider needs lots of gears to have comfortable cycling rhythm in all circumstances, the electric motor doesn't.

A question arises though...

Does the rider own a bike that has a motor for legal assist or is it a motor thats fitted to a bike (riding your armchair) ?

I like armchair

 

[jerrysimon]

I think the SRAM A2 is better suited to flatter terrains. One gear to start and one to cruise is perfect in my application and with e-assist. With a more powerful motor though, I think the application would probably work as well in hillier terrains.

I also love that I don't even need to think about changing up or down gears its all done for me.

On the Brompton ideally I could do with a few more inches in high but the chain line means I have to use a dished sprocket which only go down to 16T. The largest Brompton chain ring is 54T giving me 56" and x1.37 (the SRAM A2 multiplier) i.e. 76".

Having said all that my recent new Xootr with its derailleur 8 speed 38" - 111" is nice too. It will cruise comfortably at 21mph. For the Brompton I find that too fast, preferring to be around 16mph cruising speed.

At the end of the day I love playing with all the options gear wise, but hub gears on smaller bikes like the Brompton are definitely my preference for daily riding in crud drenched winter excursions.

Regards

Jerry

 

[RobF]

On the topic of auto shift, I see there's a Kalkhoff ebike with the electric auto version of the NuVinci hub:

Kalkhoff Sahel i360 NuVi Harmony 50cm TI 26"

 

[Kudoscycles]

On the topic of auto shift, I see there's a Kalkhoff ebike with the electric auto version of the NuVinci hub:

Kalkhoff Sahel i360 NuVi Harmony 50cm TI 26"

Thats interesting,I notice that in auto mode you select your cadence speed and the bike auto sets the gear to maintain that cadence-I wonder how that would work in practice?
So many new ideas its becoming difficult to forsee which ones will be the future?
Dave
Kudoscycles

 

[RobF]

I've read stuff about the auto NuVinci in relation to both ordinary and e bikes.

But like you, I don't quite get it.